Binder composition, mineral ore pellet and method for its preparation



United. States Patent 3,252,788 BliNDER COMPOSITION, MINERAL ORE IELLET AND METHOD FOR ITS PREPARATION Melville J. I-Iolilr, Franklin Park, Ill., assignor to International Minerals & Chemical Corporation, a corporation of New York No Drawing. Filed Feb. 19, 1963, Ser. No. 259,723

13 Claims. (Cl. 75-3) This invention relates to improvements. in the art of agglomerating finely divided mineral ore material, especially finely divided iron ore concentrates, by the wellknown pelletizing process involving'forming the finely divided ore material, in moist state, into small balls or pellets by a rolling operation and thereafter heat treating or indurating the pellets in a furnace to impart to them a considerable mechanical strength or ruggedness. In one of its aspects, this invention relatesto an improved binder composition for finely divided mineral ore materials. In another of its aspects, this invention relates to a mineral ore pellet composed of an agglomerate of finely divided ore particles held together by an improved binder composition. In still another aspect, this invention relates to a process for pelletizing finely divided mineral ore par: ticles.

In various metallurgical operations ore may be encountered in a very finely divided condition either because it occurs naturally in this condition or because it may have been reduced to this condition for the purpose of beneficiation. Typical of the latter is the situation in which taconite, a low grade iron-containing rock, is reduced to a finely divided condition and then subjected to a beneficiation procedure in order to concentrate the iron and to make available an ore of the required richness for conventional blast furnace operation.

In the further processing of such finely divided ores it is commonly necessary to agglomerate the finely divided particles into sinters, briquets, or pellets. This is particularly true in the case of taconite since the enriched taconite ore is conventionally reduced to iron in a typical blast furnace. In other metallurgical operations on other ores similar difficulties may be presented which may make it desirable to have the ore present in the form of pellets even though in its preceding processing it may have been in a very finely divided form.

While the present invention is applicable to any finely divided ore, for the purposes of illustration, it will be described with reference to taconite which may be in the form of hematite, magnetite, or mixtures of the two. In taconite processing the finely divided ore is converted into pellets which are almost spherical and have a diameter varying from one-half to one inch or more. These pellets are formed by rolling wet taconite in balling drums and then drying and indurating in a furnace. The newly formed or green pellets are usually transferred from the balling drums by conveyors or the like and thus have certain strength and elasticity requirements in order to minimize crumbling and crushing. Further, during the driving and indurating step as the moisture is driven out, a certain amount of cracking or cratering takes place tending to weaken the structural integrity of the pellets and to promote crusting which is extremely undesirable.

Because of the shortage of high grade iron ore, taconite has become important as a blast furnace feed material in consequence of which considerable efforts have been expended in the development of a commercially expedient pelletizing process. Much of the work was done by the US. Bureau of Mines. The work has been approached from the standpoint of evaluating various binders in extruding, briquetting and balling processes. See, for example, Bureau of Mines R.I. No. 3846, January 1946, wherein various binders and combinations of binders were Patented May 24, I966 tested in extruded pellets of ore slirnes. A net result of the work done was to settle upon bentonite as a binder in a balling process, generally utilizing about 13 pounds of bentonite per long ton of taconite ore, 0.65 weight percent bentonite. A typical commercial process for pelletizing taconite ores is described in U.S. Patent No. 2,743,172.

While the use of bentonite alone as a binder provides a reasonably good process for pelletizing taconite ores, there are certain problems. For example, except at concentrations of the order of magnitude of about 13 pounds per ton, there is the problem of less than nominal strength properties both in the green state and after induration. Further, the higher concentrations of bentonite necessarily result in an inherently higher silica content in the indurated pellet, thus cutting down on the grade of material fed to the blast furnace. In accordance with the present invention I have provided an improved binder which provides several significant advantages over the use of bentonite alone in the normal commercial taconite pelletizing process. For example, it permits a substantial reduction in the amount of bentonite employed without adversely affecting the strength properties of the green pellet Further, there is a substantial improvement with respect to the cratering or cracking tendency of the pellet during the drying and indurating step. Further, the reduction in the amount of bentonite permits an improvement in the grade of the fired pellet. Alternatively, my invention permits the use of a cheaper grade of bentonite, southern bentonite in lieu of western bentonite, at the same concentration level normally employed with the high grade western bentonite.

It is, therefore, an object of the present invention to provide an improved binder for agglomerating finely divided ore material.

It is another object of the present invention to provide an improved pellet of finely divided ore material, especially finely ground taconite ore.

It is still another object of the present invention to provide an improved process for the pelletizing of finely divided ore materials.

Additional objects of the present invention become apparent from the specification. v

In its broadest aspect the present invention relates to a binder composition for finely divided ore materials, especially taconite ore, containing on a dry basis from about 67 to about weight percent of bentonite uniformly mixed with from about 33 to about 5 weight percent of a water soluble soap or salt of a carboxylic acid selected from the group consisting of rosin acids, fatty acids containing from 8 to 22 carbon atoms, and mixtures of rosin and fatty acids. The bentonite employed is preferably western bentonite or a swelling type of bentonite. However, southern bentonite or non-swelling bentonite can also be employed, although less preferred. The watersoluble soap component can be the sodium, potassium or ammonium soap of rosin acids which are primarily abietic acids and its hydrogenated or dehydrogenated analogues, and fatty acids having from 8 to 22 carbon atoms such as caprylic acid, capric, lauric, myristic, palmitic, stearic, oleic, linoleic, linolenic, and mixtures of fatty acids as obtained from the hydroylsis -of animal and vegetable oils suchas tallow, cotton seed oil, corn oil, and the like, and mixtures of rosin and fatty acids such as are contained in tall oil. The sodium soaps are preferred for obvious economic reasons. An especially preferred soap for use in the binder composition of the present invention is the crude black liquor soap skimmings obtained as a by-prodnet in the kraft paper-making process, referred to hereinafter for convenience as crude kraft soap skimmings. The chemical composition of crude kraft soap skimmings is well known and can be found in most handbooks on the subject of paper chemistry. In general, crude kraft soap skimmings on a dry basis contain from about 85 to about 95% by weight of the sodium soaps of about equal parts of rosin acids and C to C fatty acids, primarily oleic and linoleic acids and some palmitic, the remainder being unsaponifiables such as alcohols, sterols and lignins.

On a total basis commercial crude kraft soap skimmings,

as ordinarily supplied, contain up to about 40% moisture, about 51 to about 57 weight percent sodium soaps, and about 3 to about 9 weight percent of unsaponifiables. Crude kraft soap skimmings are to be distinguished from tall oil which is a mixture of the free fatty and rosin acids produced from the soap skirnmings by acidification thereof. It will be appreciated, therefore, that saponified tall oil can be employed in my binder composition but is less preferred for economic reasons.

In the preparation of my improved binder composition, it is important that the water-soluble soap component and the bentonite component be in substantially homogeneous admixture. While conventional paddle mixers can be employed in the blending operation, the preferred procedure is to eifect admixture in a grinding device such as a ball mill, a hammer mill or a ring and roller mixer. Through the use of equipment of this type there is reasonable assurance of forming a fine coating of soap film over the individual bentonite particles. Further, the use of devices of this type substantially reduces the need for further comminution of the binder composition.

Thus, in a preferred embodiment, my improved binder composition is prepared by blending from about 10 to about 20 weight percent, preferably about 15.5 weight percent of commercial crude kraft soap skimmings with about 84.5 weight percent of western bentonite in a conventional ball mill. The time of mixing and grinding is not critical, but should be carried out for a period sufficient to insure a substantially homogeneous admixture.

In the blending operation the soap employed may be dry or be wet, but the amount of water present in the blending operation should not exceed the moisture absorption capacity of the bentonite, since otherwise the bentonite will tend to swell and gel to form a pasty mixture.

In the preparation of pellets from finely divided mineral ore particles in accordance with the present invention by the conventional balling process, about 0.3 to about 1.0 weight percent, preferably about 0.35 to about 0.45 weight percent on a dry basis, of the binder composition described hereinabove is mixed with the finely divided ore particles, which for purposes of illustration will be taconite. The blending can take place prior to admission to a conventional pelletizer such as a disc pelletizer or a rolling drum pelletizer, to form seed pellets which are enlarged to a desirable size as the balling operation continues. Alternatively, finely ground bentonite and the taconite ore particles may be blended and sprayed with an aqueous solution of the soap composition described hereinbefore.

It will be appreciated that the quantities of bentonite and soap employed will be within the ranges described hereinbefore when this procedure is employed. The preferred procedure is to blend moist ore particles containing preferably not more than about 10 to 12% moisture with the prepared binder composition described hereinbefore in a disc, pan or drum pelletizer where there is first formed small seed pellets which grow, by accretion, to a size useful for metallurgical purposes. Pellets of the desired size are discharged from the pelletizer and are then transferred to a furnace for heat treatment or induration. I have found that the binder composition of the present invention very materially adds to the mechanical strength or ruggedness of the green pellets, which added mechanical strength carries through the drying of the pellets and into the incipient induration stage of the heat treatment. Further, I have found that the use of my binder minimizes considerably the exfoliation, cracking or cratering of the pellets during the drying and heating stage, thus minimizing the formation of undesirable fines as compared to when the bentonite alone is used as the bender.

The following examples are intended to be illustrative of the underlying principles of the present invention and are not to be construed as unduly limiting thereof.

EXAMPLE I A mixture of 4 parts of Wyoming bentonite and 1 part of commercial crude kraft soap skimmings containing about 40% moisture was prepared by grinding to a homogeneous mixture in a mortar and pestle. This mixture was a dark tan powder. It was intimately mixed with dry magnetite ore at 0.44% (8.8 lbs. per ton of magnetite) and formed into pellets by rolling in a revolving pan pelletizer, adding water as needed to develop the pellet formation as is known in the art. Table I shows the elfect of the soap-skimmings addition.

Table I BENTONITE-SOAP SKIMMING 4:1 MIXTURE IN MAGNET- ITE PELLETS A mixture of 55 lbs. of commercial crude kraft soapskimmings containing about 40% moisture was mulled into 300 lbs. of bentonite, dried, and ball-milled for sixteen hours. Pellets were fonmed from dry magnetite in the balling device by alternately feeding a mixture of the ore containing 0.415% of the bentonite mixture (8.3 lbs./ ton ore) with water spray until pellets of the desired size were formed. Table II shows the results of this test.

Table II MAGNETITE PELLETS WITH BENTONITE CONTAINING 15.5% COMMERCIAL SOAP SKIMMINGS 4 Drop test Com- Bmder Perpression Percent cent strength, water 10 18" pounds Bentonite. 15.5%:

Soap skimmings 0. 415 7. 8 3. 88 1. 57 7. 14 Do 0. 415 7. 3 3. 4 1. 45 7. 27 14. 6 6. 2 1. 67 7. 10 8. 3 3. 6 1. 83 8. 37 4. 1 2. 17 1. 52 7. 27 3. 9 2. 0 1. 395 7. 69

EXAMPLE III Using the mixture of 4 parts bentonite to 1 pant soap skimmings as in Example I, pellets were prepared using hematite ore instead of magnetite. The results are tabulated in Table III.

Table III SOAP SKIMMINGS IN HEMATITE ORE PELLETS 0.44% BEN TONITE Soap 0.65% skimmings 4:1 bentonite 10 drops 8. 875 7. 70 18" drops 4.625 4. 63 Compression strength, lbs 1.06 0.88 H20 content, percent 6. 67 7. 0O

5 EXAMPLEIV Distilled tall oil fatty acid heads containing 5% rosin were neutralized with sodium hydroxide and sprayed from 10% solution in ethanol and water onto powdered magnetite ore and bentonite in an amount sufficient to deposit desired levels of the sodium tallate. Pellets were then formed as in preceding examples.

Table IV GREEN MAGNETITE PELLETS USING SODIUM TALLATE WITH BENTONITE Pellets for-med using modified bentonite binder according to Example I at 0.44% and another run containing straight bentonite at 0.65% were charged into a furnace at 285 F. The temperature was raised to 750 F. in 19 minutes. The bentonite containing pellets cracked badly, whereas pellets containing the modified bentonite binder were in good condition.

A similar set of pellets was changed into a muiile furnace at 215 F. and heatedto 750 F. in fifteen minutes, held 15 minutes, and transferred to a furnace at 2200 F., for one half hour. Such treatment caused the bentonitecontaining pellets to crack badly, whereas pellets containing the modified bentonite retained their original appear- EXAMPLE VI Non-swelling bentonites were used in pellet formation as in Example IV in place of Wyoming bentonite. The effect of sodium tallate is shown in Table V.

Table V MAGNETITE PELLETS WITH NON-SWELLING BENTONITES Drop test Compres- Bentonite type Persion Percent cent strength, water 10 18 pounds High pH Aberdeen 0. 65 4. 2.0 1. 08 7.12 0 Switzerland 0.65 3. 2. 0 1. 38 7.24 Dixie Bond Standard 0. 65 3.0 2.0 1.01 6. 80 0 Switzerland plus 0.142

Na tallate 0.65 5. 6 2. 7 1. 40 6. 84 Dixie Bond Standard plus 0.158 Na tallate 0.65 5. 6 2. 8 1. 08 5. 97 Regular Stendard 0.65 4.1 2. 2 1. 52 7. 27

While this invention has been described and exemplified in terms of its preferred embodiment, modifications can be made without departing trom the spirit and scope of the invention.

1 claim:

1. A binder composition for mineral ore pellets comprising a substantially homogeneous mixture containing on a dry basis from about 67 to about 95 weight percent of bentonite and from about 33 to about 5 weight percent of'a water-soluble soap of a carboxylic acid selected from the group consisting of rosin acids, fatty acids having from 8 to 22 carbon atoms, mixtures of said fatty acids, and mixtures of said fatty acids and rosin acids.

2. A binder composition according to claim 1 wherein said soaps are sodium soaps.

3. A binder composition for finely divided mineral ore pellets comprising a substantially homogeneous mixture containing on a dry basis from about 67 to about 95 weight percent of western bentonite and from about 33 to about 5 weight percent of water-soluble soaps of a mixture of about equal parts by weight of rosin acids and C to C fatty acids.

4. A binder composition for finely divided taconite ore pellets comprising a substantially homogeneous mixture containing from about to about weight percent of western bentonile and from about 20 to about 10' weight percent of commercial crude kraft soap skimmings 5. A binder composition according to claim 4 containing about 84.5 weight percent of western bentonite and about 15.5 weight percent of commercial crude kraft soap skimmings.

6. A mineral ore pellet composed of an agglomerate of finely divided ore particles held together with from about 03 to about 1% by weight of a binder composition comprising on a dry basis, from about 67 to about percent by weight of bentonite and from about 33 to about 5 percent by weight of a water-soluble soap of a carboxylic acid selected from the group consisting of rosin acids, fatty acids containing from 8 to about 22 carbon atoms, mixtures of said fatty acids and mixtures of said fatty acids and rosin acids.

7. A mineral ore pellet according to claim 6 wherein said mineral ore is taconite.

8. A taconite pellet comprising finely divided taconite particles held together with from about 0.3 to about 1% by weight of a binder comprising, on a dry basis, from about 67 to about 95 percent by weight of bentonite and from about 33 to about 5 percent by weight of the sodium soaps of a carboxylic acid selected from the group consisting of rosin acids, C to C fatty acids, mixtures of said fatty acids, and mixtures of said fatty acids and rosin acids.

9. A taconite pellet comprising finely divided taconite particles held together with about 0.35 to about 1.0 percent by weight of a binder containing, on a dry basis, from about 67 to about 95 percent by weight of bentonite and from about 33 to about 5 percent by weight of the sodium soaps of a mixture of approximately equal parts by weight of rosin acids and C to C fatty acids.

10. A taconite pellet comprising finely divided taconite particles held together with about 0.44 percent by weight of a binder containing from about 80 to about 90 percent by weight of bentonite and from about 20 to about 10 percent by weight of commercial crude kraft soap skimmings.

11. A taconite pellet according to claim 10 wherein said binder contains about 94.5 percent by weight of bentonite and about 15.5 percent by weight of commercial crude kratt soap skimmings.

12. A method for the preparation of pellets of finely divided ore material which comprises forming a homogeneous plastic mixture containing, on a dry basis, the finely divided ore particles, from about 0.29 to about 0.96 percent of bentonite, and from about 0.04 to about 0.26 weight percent of a water-soluble soap of a carboxylic acid selected from the group consisting of rosin acids, fatty acids having from 8 to 22 carbon atoms, mixtures of said fatty acids and mixtures of said rosin and fatty acids, forming the resulting homogeneous mixture into small masses, protractedly rolling the small masses in. conventional rotary pelletizing apparatus into raw pellets of at least 4 inch in diameter, and recovering said raw pellets therefrom.

7 8 13. A method according to claim 12 wherein the finely 2,833,642 5/ 1958 Barker et al. 753 divided ore material is taconite and the Water-soluble soap 2,833,659 5/1958 Bauer 106-123 is commercial crude kraft soap skimmings. 2,914,395 11/ 1959 Davies 75-3 References Cited by the Examiner 5 I FOREIGN PATENTS UNITED STATES PATENTS v533,975 12/ 1956 Canada.

Edison L- Primary Examiner.

2,220,385 11/1940 Abbott et a1 '7555 BENJAMIN HENKIN, Examiner. 

8. A TACONITE PELLET COMPRISING FINELY DIVIDED TACONITE PARTICLES HELD TOGETHER WITH FROM ABOUT 0.3 TO ABOUT 1% BY WEIGHT OF A BINDER COMPRISING, ON A DRY BASIS, FROM ABOUT 67 TO ABOUT 95 PERCENT BY WEIGHT OF BENTONITE AND FROM ABOUT 33 TO ABOUT 5 PERCENT BY WEIGHT OF THE SODIUM SOAPS OF A CARBOXYLIC ACID SELECTED FROM THE GROUP CONSISTING OF ROSIN ACIDS, C16 TO C18 FATTY ACIDS, MIXTURES OF SAID FATTY ACIDS, AND MIXTURES OF SAID FATTY ACIDS AND ROSIN ACIDS. 